Air conditioning systems of the type typically employed in vehicles, utilize a heat exchanger (sometimes referred to an evaporator) to cool the air within the passenger compartment of the vehicle. The evaporator includes one or more internal passages for allowing the flow of refrigeration fluid therethrough. Air is passed over an outside surface of the evaporator and the heat from the air is transferred to the refrigeration fluid as it passes through and evaporates within the evaporator. The refrigerant is forced through the evaporator by a refrigerant pump, commonly referred to as a compressor. The compressor is typically coupled to the engine by way of a belt drive and an electric clutch. The electric clutch engages the compressor to the engine when an electric current is applied to the clutch and disengages the compressor from the engine when the electric current ceases to flow through the clutch. Thus, the electric clutch forms a convenient means of engaging and disengaging the compressor.
A temperature sensing device is typically located on the surface of the evaporator to sense the temperature of the evaporator. This temperature information is used to control the compressor clutch so that the temperature of the evaporator can be controlled.
Various control schemes are known for controlling the temperature of the evaporator. One control scheme for controlling the temperature of the evaporator involves cycling the compressor clutch on and off as the sole means of controlling evaporator temperature. Systems that employ this type of control scheme have a problem known as fogging. Fogging involves the expelling of visible water vapor from the ventilation system of the vehicle. Fogging occurs when the dew point temperature of the air passing through the evaporator is reached. This can occur at localized portions of the evaporator if these localized locations are sufficiently cold, or it can occur if the evaporator, as a whole is too cold.
In the case where localized cold spots are responsible for causing fogging, this typically occurs when the compressor is first turned on after a relatively long period of not operating. Under these conditions, refrigerant flows through the evaporator, rapidly cooling its various surfaces and causing its surfaces to cool at differing rates. As has been already explained, this promotes fogging. The present invention minimizes, or eliminates, fogging by controlling the rate at which initial cooling of the evaporator takes place. This allows the different evaporator surfaces to cool at substantially the same rate and therefore no visible water vapor is expelled.
Thus, it is an object of this invention to set forth a system which controls fogging in an air conditioning system.
It is a further object of this invention to disclose an anti-fogging methodology in which the rate of initial cooling of the evaporator is not compromised.